In order to provide for safety consideration of conventional explosives used for open cast or strip mining, quarry blasting or construction blasting, such explosives typically comprise explosive compounds which are insensitive to initiation by a detonator. In order to be capable of initiating the explosive material, a principle known as the “explosives train” is employed, wherein energy released by a detonator is transferred to an intermediate charge or “booster”, which is sufficiently sensitive to be initiated by the detonator, and which then amplifies the energy so as to initiate the explosive compound of the main charge or blasting agent.
Various boosters have been proposed in the prior art and generally comprise an elongate hollow body, typically of a plastics or cardboard material, which is filled with an explosive material that is more sensitive than that of the main charge. The body commonly includes an appropriate formation, also known as a detonator well, for receiving a detonator such that the detonator is positioned appropriately so as to ensure reliable initiation of the explosives material of the booster.
Effectiveness of explosives is largely dependent on the rate at which the potential energy contained in the explosive material can be released. Thus, in order for an explosive to function optimally, a maximum amount of explosive material should be initiated in the shortest possible time.
The manner in which a detonation wave initiates explosive material can be tailored. U.S. Pat. No. 2,604,042 describes a method of converting a point source shock wave into a plane wave by tailoring the shape of the explosive material so that it is cone-shaped. The method involves machining the explosive material into shape. Complicated and costly machinery is necessary to ensure safety during the machining of the explosive material.
A similar cone-shaped arrangement of explosives is described in PCT International Publication number WO99/53264. A booster is described which includes two explosive charges, wherein the first explosive charge is sensitive to ignition and the second explosive charge is less sensitive to ignition. The booster is ice-cream cone-shaped which shapes the shock wave.
U.S. Pat. No. 4,729,318 describes an explosive plane-wave air lens which uses a disc-shaped impactor that spans between donor and acceptor explosives with different detonation velocities to convert a detonation wave from one wave form to another.
In this specification, “detonator” shall have its widest meaning and shall include any suitable form of initiation commonly used for commercial blasting including, but not limited to, non-electric detonators such as shock tube detonators or fuse caps, electric detonators such as instantaneous electrical detonators (IED) or exploding foil detonators (EFI), and electronic detonators.
Further, “detonation cable” shall have the widest meaning and shall include any suitable means of transmitting a detonating signal to the detonator, including, but not limited to, detonation cord, electronic or electric wire, shock tube, optic fibre cable, electric conductor and the like.